Automatic radio compass



Sept. Z1, 1948. H. F. PENFOLD E'rm. 2,449,859

AUTOMATIC RADIO COMPASS lFiled Jan) 2n 1944 s sheets-sheet 1 sept 2, 1948. H. F. PENFOLD Erm. 2,449,859

AUTOMATIC RADIO COMPASS Filed Jn. 27, 1944 5 Sheets-Sheet 2 Ill l' Sept.21,1948. H. F. PENFOLD ETAL 2,449,859

' AUTOMATIC RADIO COMPASS I Filed Jan. 27, 1944 3 Sheets-Sheet 3 00P ra //v/f a- "o/v caafzsf Pas/Wam" W www WM @ya U fr mm Patented Sept. 2l, 1948 AUTOMATIC RADIO COMPASS miliare F. Pentola, Flushing, and Joseph P. nella. Corte, Forest Hills, N. Y., assignors to Fairchild Camera and Instrument Corporation, a corpo ration oi' Delaware Application January 27, 1944, Serial No. 519,880

6 Claims.

t l This invention relates to applicable to various uses. It is well adapted for use as an automatic loop director for radio compasses, and it will be disclosed and discussed in that connection.

Radio compasses of known type receive on two antennae the incoming signal to which the compass is tuned. One antenna is non-directional: the other is a directional or loop antenna. With an incoming signal of given strength, the loop antenna current varies as the plane of the loop 1s shifted to different angular positions with respect to the direction from which the signal is arriving. A radio compass utilizes this wellknown effect to determine or indicate the signal's direction. 'I'he output of the compass circuit varies in distinctive manner (e. g. phase reversal) as the plane of the loop is shifted to and slightly past the on course position in which it is at right angles with the signal direction. As-

` sociated with the loop is an azimuth indicator which, when the loop is "on course, points in the direction from which the signal is arriving. When applied to a radio compass, the present invention utilizes the phase of the loop current in governing the rotation of the loop to on course position. The phase reversal as the on course position is passed is utilized' to return the loop to on course.

A general object of the invention is to. provide anA accurate, sensitive follow-up system which l provides ample power` for follow-up purposes, in

response to variations in weak or lower level energy.

Another object of the invention is to4 provide a follow-up system whichprovides substantially full follow-up power the instant such power is called for by the change in the conditions which initiates the follow-up.

A further object of the invention is to providea sensitive, accurate, and reliable follow-up system for automatically directing the loop antenna of a radio compass.

A still further object of the invention is to provide a follow-up system providing ample follow-up power in response to even relatively weak initiating current, the direction of the follow-up action being determined by the phase of such current.

Various additional objects of the invention will be apparent to those skilled in the art. from a consideration of the following disclosure.

Fig. 1 of the drawings is a schematic diagram showing a follow-up system or circuit of the presa follow-up system A ent invention applied as an automatic loop director for a known type of radio compass.

Figs. 1A through 7A show related voltages or currents in that vpart of the control circuit which leads to one saturable control reactor that is connected into the motor-circuit of the follow-up motor. These curves apply when the loop is to the left of on course position.

Figs. 1B through 7B show similarly related voltages or currents in that part of the control circuit which leads to the other saturable control reactor that is connected into the motor circuit. These curves also apply when the loop is to the left of on course" position.

Figs. 1C through 7C correspond respectively to Figs. lA through 7A, but apply when the loop is to the right of on course" position.

Figs. 1D through 7D correspond respectively to y Figs. 1B through 7B, but apply when the loop is to the right of on course position.

A brief preliminary outline of the manner in which the invention operates, will be helpful in understanding the detailed description which follows later.

A local audio frequency oscillator I is used as a source of flxed phase-reference voltage. The energy received by the loop antenna 2 is modulated at 3 by a voltage obtained from local source I. The modulated radio frequency loop voltage is 'combined with the radio frequency voltage from the non-directional antenna, and then detected at 4. The means for carrying out these stepsare known in the art. s

The detected modulating voltage En issues either in phase with or in phase opposition to the reference voltage El depending upon whether the normal to the plane of the loop-is to the left or rig'ht of the line on which the signal is arriving. Voltages derived from the detected modulating voltage E2 and the reference voltage E1 are combined in phase or 'in phase opposition to supply a diilerential bias to the grids of the two electronic tubes VT-4 and VT--5 such that the plate current of one or the other, but not both, increases depending on whether the loop is to the left or to the right ofthe fon course bearing. The plate current is made to ilow through and saturate a control reactor T3 or T4, in series witi; one field of a balanced two phase motor M causing Aupset of the balance and consequent rotation of the motor in the direction necessary to move the loop to the correct bearing or on course" position., The motor M is. of course, mechanically connected to loop 2, so as to rotate the loop.

This is indicated schematically in Fig. 1 of the drawing, it being evident that such reducing 4 the positive half cycles of voltage E2" are sup significant positive excursion, current Is woul opposition to reference voltage E1, depending upon whether the loop is to the left or to the right of on course position.

The reference voltage E1 is applied to transformer T1 whose ,center tapped secondary provides voltages E1 and E1. Figures 1A and 1B (also Figs. 1C and 1D) show three cycles of sinusoids E1' and E1", respectively. The voltages E1 and E1 are applied to rectiers VT-I and VT-2 in phase opposition with respect to the center tap CT of the transformer T1. The reotifiers VT-I and VT2 are so poled as to rectify those pulses of E1' and E1" which are negative to the point CT. Figures 2A and 2B illustrate the voltages developed across resistances R1 and Rz respectively by the rectified current. These voltages IR1 and IR: are applied respectively to grid G4 of vacuum tube VT-4 and grid G5 of vacuum tube VT-5. All the voltages shown in Figs. 1A, 1B, 2A and 2B have as their base or reference, point CT, which, is the same as ground point GRD. The relationship set forth in this paragraph apply regardless of whether the loop is to the left or the right of the on course bearing. Thus Fig. 1C is a duplicate of Fig. 1A, and Fig. 1D is a duplicate of Fig. 1B.

lVoltage E2, the nature of which has been already explained, is applied to transformer T2. To the secondary of transformer T2 is connected a series circuit of resistor R3, a rectier VT-3 and a battery B. The solid line curves of Figs. 3A and 3B illustrate the voltage E2 which is developed directly across the secondary of transformer T2 and which is phased for the displacement of the loop to the left of the on course position. The control voltage E2" which develops across the rectifier VT-3 is illustrated in both Figs. 4A and 4B. This voltage Ez" is added vectorially to the voltages developed across resistances R1 and R2 (see Figs. 2A and 2B) to produce a differential bias on grids G4 and G5 of vacuum tubes VT-4 and VT-5.

Comparing the dotted curve of Fig. 4A with thel dotted curve of Fig. 3A, or that of Fig. 4B with the dotted curve of Fig. 3B, it will be apparent that voltage Ez" has had its positive half cycles partly suppressed. This suppression is eiected by resistance R3, the delay voltage battery and rectifier VT-3, this rectier being poled to pass current which is positive with respect to GRD. During the negative half cycles no significant amount of current ows through rectier VT-3, which permits voltage E2" to reach its normal maximum value. The positive half cycles also pass through unattenuated by the rectifier so long as their peak value remains less than the delay voltage Es. AThis is readily seen by comparing the solid curves of Figures 3A and 4A and those of Figures 3B and 4B. However, if the peak exceeds the delay voltage, during that portion of the positive cycle when the delay voltage is overcome, the impedance of the rectier VT-3 is lowered. Thus ow interfering with the action of current I4 ii unbalancing the motor bridge circuit which is t be explained later.

The control, voltage En" is vectorially added t the voltage developed across resistance R1 to pro duce voltage E4, which is applied to grid G4. Ad ditionally the same voltage Ez" is vectoriall; added to the voltage developed across resistanc R2 to produce voltage E5, which is applied to gri Gs. Voltage E4 is shown in Fig. 5A,being the vecto sum of the voltages of Figs. 2A and 4A. Voltag E5 is shown in Fig. 5B, being the vector sum o the voltages shown in Figs. 2B and 4B.

The vacuum tubes VT4 and VT-S are nor mally blocked, i. e., pass very little or no curreni This may be eiected by suitable negative bias o the grids or by the use of tubes whose plate cur rent is nil with zero grid bias. As shown in Fig 5B voltage Es has no positive portion, and henc no slgnicant amount of current flows in th plate circuit of tube VT-5. This is indicated i1 solid lines in Fig. 6B which shows the plate cur rent Is in solid lines. However, voltage E4 doe have positive half cycles, and these applied t grid G4 result in plate current I4 shown in Fig. 6A Condensers C1 and C2 partially smooth out th currrent delivered to the primaries of the satur a-ble control reactors T3 and T4, e. g. to the forr shown in Fig. 7A. With the loop to the left o on course position the current delivered to th primary of reactor T4 is zero, as shown in soli line in Fig. 7B.

The energization of reactor Ts, with no ener gization of reactor T4, causes motor M to rotat in the direction to move the loop to the right, t bring the loop on course. The motor actioz will be described later.

If the loop be to the right of on course posi tion, Figs. 1C through '7C and 1D through 7l will apply. In this case the loop current is re versed and accordingly voltage E2' is like wise reversed 180, as shown in Figs. 3C and 3l: Control voltage E2" is then as shown in Figs. 4( and 4D. The vector sum of voltage E2" (Fig. 4C and voltage IR1 (Fig. 2C) gives the voltage E shown in Fig. 5C. This has no positive portion and hen-ce the plate current I4 of tube VT-i is very small or practically nil, as shown in Fig 6C. However, the vector sum of volt-age Ez (Fig. 4D) and voltage IRz (Fig. 2D) give voltage Es as shown in Fig. 5D. This produce` plate current I5 (Fig. 6D). which is smoothed b; condenser C2 and energizes the primary of reactoi T4 as indicated in Fig. 7D. The motor now ro tates in the direction to move the loop 2 to th left, to bring the loop on course.

The motor M is a two-phase motor having iield` F1 and F2 connected in balanced bridge relation ship with the secondaries of the saturable control reactors Ta and T4. Condenser C3 aids i1 phasing the voltage applied to the second phas of the motor. Reactors Ta and T4 are so wo'un( that their windings which arein series with field: F1 and F2 produce zero ux in the respective pril mary windings when the A. C. supply voltage i: applied to the motor. This Vprecludes the possi- :afi-tastov bility of any A. C. motor supply voltage developing in the plate circuits VT-4 and VT-B and interfering with their operation.

The bridge formed by eld windings F1 and F: and reactor secondaries ST3 and ST4 is balanced when plate currents I4 and I5 are either the same or zero. In this condition motor M is not effectivelyenergized and hence it remains stationary. When plate current I4 ilowsit saturates the core of reactor Ta, thereby lowering the impedance of its secondary winding ST3. This so unbalances the bridge that field F1 receives a voltage approximately equal to but out of phase with that of field Fu; and the motor M rotates in the proper direction. When plate current Is flows (current I4 then being small or zero), the core of reactor T4. is saturated, and the bridge is similarly unbalanced in the opposite direction. Thus, the motor rotates in the opposite direction.

In compliance with the patent statutes we Ihave disclosed the best' form in which We have contemplated applying our invention, but it will be realized that the disclosure is illustrative and limiting.

What we claim is:

1. An automatic loop director for a radio compass. comprising: an alternating current power source; a reversible motor for turning the loop in either direction to place it on course; a motor circuit connecting the 'motor to the power source, the motor circuit being normally balanced for keeping the motor operatively deenergized; a source of phase-reference voltage separate from said alternating current power source; an intermediate circuit connecting the phase-reference source to the motor circuit, said intermediate circuit being normally balanced for maintaining the balance of the motor circuit; means for deriving a control voltage in phase with the reference voltage when the loop is oil. course in one ldirection and in phase opposition to the reference voltage when the loop is off course in the other direction; and means for applying the control voltage to the intermediate circuit for upsetting the balance of the motor circuit in one direction when the control voltage is in phase with the reference voltage and for upsetting the balance of the motor circuit in the other direction when the control voltage is in phase opposition to the reference voltage, whereby the motor is energized for rotation in either direction as required to place the loop on course.

2. An automatic loop director for a radio compass, comprising: a reversible electric motor for turning the loop in either direction to place it not on course, said motor having two eld windings;`

a pair of plural-winding saturable-core reactors; a four-arm bridge circuit having said motor windings connected into two of the arms and having windings of the respective reactors connected into the other two arms; a source of electric power connected to a diagonal of the bridge, the bridge being normally balanced for keeping the motor operatively deenergized; a source of phase-reference voltage; a normally balanced intermediate circuit connecting the reference voltage source to windings of both reactors; means for deriving a control voltage in phase with the reference voltage when the loop is off course in one direction and in phase opposition to the reference voltage when the loop is oi course in the other direction; and means for impressing the control voltage on the intermediate circuit for selectively increasing the saturation eiect of said reactors according to the aforesaid phase relawhen the loop is on course in either direction and the motor is energized for rotation to place the loop on course,

3. An'automatic loop director for a radio con`i-l pass, comprising: an electric power source; ja reversible motor for turning the loop in either direction to place it on course; a motor circuit connecting the motor tothe power source. the motor circuit being normally balanced for keeping the motor operatively deenergized; a pair of saturable-core reactors connected into the motor circuitand operative when selectively energized to unbalance the motor circuit in opposite directions; a pair ofwgrid-controlled electric valves connected to the reactors for energizing the same; a `source of phase-reference voltage; an intermediate circuit connecting the reference voltage source to the grids of the electric valves and operable to impress on the grids of thel respective valves negative half cycles of voltage degrees out of phase; means for deriving a control voltage in phase with the reference voltage when the loop is o course in one direction and in phase opposition to the reference age to the grid of one valve only when the loop is oii course, in` one direction and positive half cycles of voltage to the grid of the other valve only when the loop is ofi course in the other direction, whereby the reactors are -`selectively' energized when the loop is ofi course in either direction and the motor is energized for rotation to place the loop on course.

4. An automatic loop director for a radio cornpass, comprising: a motor for turning the loop in either direction to place it on course; a source of power for the motor; a motor circuit connecting the source of power to the motor, the motor .circuit being normally balanced for keeping the motor operatively deenergized; a pair of normally blocked grid-controlled valves connected to unbalance the motor circuit in opposite directions when the valves are rendered conducting selectively; avsource of phase-reference voltage, said source being independent from said source of power; means for deriving a control voltage in phase with the reference voltage when the loop is o course in one direction and in phase opposition to the reference voltage when the loop is off course in the opposite direction; and a circuit for vectorially combining the control voltage and the reference voltage and applying a positive resultant thereof to the grids of the.

in either direction and the motoris energizedto place the loop on course.

5. An automatic loop director for a radio compass, comprising: a motor for turning the loop in either direction to place it on course; a source of power for the motor; a motor circuit connecting the source of power to the motor, the motor circuit being normally balanced for keeping the motor operatively deenergized; a pair of saturable-core reactors connected into the motor circuit, said reactors being operative when selectively energized to unbalance the motor circuit in opposite directions; a pair of normally blocked grid-controlled valves connected to the reactors respectively for selectively energizing .them when the valves are rendered conducting selectively; a source of phase-reference voltage; means for deriving a contrl voltage in phase with the reference voltage when the loop is of! course in one direction and in phase opposition tothe reference voltage when the loop is off course in the opposite direction; and a circuit for vectorially combining the control voltage and the reference voltage and applying a positive resultant thereof to the grids of the valves selectively according to the aforesaid phase relation of the control voltage to the reference voltage, xwhereby the valves are rendered conducting selectively 'when the loop is off course in'either Vdirection and the reactors are energized selec- -tively and the motor is energized to place the loop on course.

6. An automatic direction finding system, comprising: a directional rotatable antenna; a reversible motor connected to said antenna; a first ,source of alternating voltage for driving said motor; a second source oi' alternating voltage .sep-

arate from said first source for phase reference; means responsive to the position of said antenna relative to the direction of propagation of a received signal for producing a control signal having the same frequency as said second source and having a phase angle of zero or 180 degrees. relative thereto depending upon the rotational position of said antenna; a comparison circuit including' rectication means for producing from said second source of alternating voltage a rst andra second comparison voltage, said rst voltage constituting negative pulses each separated by an interval of time substantially equal to the duration of one of said pulses, said second voltage constituting similarly spaced negative pulses occurring during the interval of time between successive pulses of said rst comparison voltage, and means for vectorially combining said file of this patent:

control voltage with each of said iii-st and second 1 comparison voltages thereby producing two resultant signals one or the other of which has its positive peaks suppressed in accordance with the phase relationship between said control voltage and said comparison voltages` and consequently in accordance with' the rotational position of said antenna; a bridge circuit comprising at least two windings of said motor and two similar variable impedance elements and connected to said first source of alternating voltage whereby the rotation and direction of rotation of said motor are controlled by the relative impedances of said variable impedance elements; and two impedance control means each coupled to one of saidresultant signals and each operative to vary the impedance of the one of said impedance elements associated therewith in accordance with the magnitude of the positive peaks of the respective resultant signal.

HILLIARD F. PENFOLD. JOSEPH P. DELLA CORTE.

REFERENCES CITED The following references are of record in the UNITED STATES PATENTS 

